Flexures are used to connect two members of a system between which a relatively small movement is required. This method of construction has a great advantage of simplicity, coupled with a complete freedom from friction and backlash, which are very detrimental to the performance of said system.
The great advantage of the flexure lies in the absence of sliding parts. Consequently, there is not need of lubrication. Neither friction nor wear occur, and dirt, if any, does not cause trouble.
The use of an arrangement in which the shaft, drawbar and restoring spring are essentially one, minimizes any relative positional change during and after operation.
In recent years, with development of computer controlled numeric machines, a great need has arisen for very accurate spindles for use in drilling, milling, grinding, dicing, and other machining-type operations. With the greater use of new types of cutting materials such as tungsten carbide, aluminum oxide, and other ceramics which are not being utilized in cutting tools, increasingly higher speeds are desired. However, most, if not all of these new materials are brittle, and therefore it is desirable to minimize any shock associated with high speed rotating cutting tools. Moreover, in certain types of drilling operations, rotational speeds up to about 120,000 rpm are used and under circumstances in which the rotation of the spindle must be extremely accurate.
The desirability of obtaining the lowest possible tool shock and high accuracy dictates a spindle design which obtains and maintains an accurate axis of rotation which does not deviate during operation. Low spindle vibration is also desirable for the same reasons.
One of the difficulties with machined integral springs is that there is a tendency, after extended cycles of compressions and relaxation, or elongation and relaxation, for certain portions of the structure to exhibit fatigue failure. Since the advantages of a machined spring, as herein described for the purposes described, are significant, experimental testing has indicated that the life of the spring may be extended significantly if the stresses in the spring structure can be more uniformly distributed.
Thus, for example, the spring structure of the previously filed application above identified operates in a manner which is quite acceptable. The improved structure of this invention constitutes an improvement in the structure previously described and is believed to represent an improvement generally in the structure of integral machined one-piece springs.
In effect, the improvements of this invention relate to a structure in which the stresses are more evenly distributed so as to assure essentially an even stress distribution in the spring structure. As will be described in detail, this structure involves modification of the slot widths in selected regions of the spring and providing controlled radial dimensions of the lands so that the spring is not subject to high localized and uneven stresses which tend to promote failure at certain regions of the spring. The result is a much improved machined spring structure having use in a much wider field than merely high speed spindles.
Further details of these and other novel features of the invention including, for example, its structural and method cooperation with other system embodiments, as well as additional objects and advantages of the invention and their principles of operation will become apparent and be best understood from a consideration of the following description, when taken in connection with the accompanying drawing, which is presented by way of an illustrative example only.